Bluetooth: Track the LE Identity Address in struct hci_conn

Since we want user space to see and use the LE Identity Address whenever
interfacing with the kernel it makes sense to track that instead of the
real address (the two will only be different in the case of an RPA).
This patch adds the necessary updates to when an LE connection gets
established and when receiving the Identity Address from a remote
device.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>